Method and apparatus for burning carbonaceous fuels



Dec. 7, 1948. R. A. SHERMAN METHOD-AND APPARATUS FOR BURNING CARBONACEQUS FUELS 2 Sheets-Sheet 1 Filed June 30, 1944 29 Q 26 W! 65 D I 6O l2 1 GI /13 33 63 9 I3 I v ,L m 34 79 QQ a.

2 Sl1eets-$heet 2 INVE/VTUR Ralph A. Sherman ATTORNEYS R. A SHERMAN Dec. 7, 1948.

METHOD AND APPARATUS FOR BURNING CARBONACEOUS FUELS Filed June 30, 1944 Patented Dec. 7, 1948 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR BURNING CARBONACEOUS FUELS tion of Delaware Application June 30, 1944, Serial No. 543,010

9 Claims. (Cl. 110-45) This invention relates to a method and apparatus for burning solid fuels which is designed with a view to its application and use for the operation of residential heating furnaces or industrial boiler furnaces, with maximum production of heating units from a given quantity of fuel and the efficient transfer thereof, with minimum loss, to the medium to be heated. f

The subject matter of the present application constitutes, in part, a continuation of my pending application for patent, Serial No. 378,298, filed February 10, 1941, now Patent No. 2,371,191, granted March 13, 1945.

Several types of automatic stokers have heretofore been developed for the feeding of coal to be burned on the furnace grate. In the operation of such stokers the method of burning the coal is similar and is characterized by the feeding of the coal upwardly through a retort, together with combustion air admitted at the bottom thereof and, in some cases, the provision 02 one or more rows of tuyeres or jet orifices at the top of the retort to which air is supplied from a fan or blower.

It is a well known fact that .bituminous coals, when heated to high temperatures, become, more or less plastic and swell or expand so that adiacent particles will coalesce or agglomerate intoglarge the coke column. As is well known, the tempera ture developed in a fuel bed is directly proportional to the rate of burning per unit of burning area. Accordingly, since this burning area is restricted to a-narrow ring at the base of the coke column extremely high fuel bed temperatures are developed, this condition being augmented by the fact that since the coke bed extends above the tuyeres, the developed heat cannot be radiated to the relatively cool heat transfer surfaces of the furnace or boiler.

The high fuel bed temperatures which are inherent in the operating principles of prior art stokers make it necessary to remove the ash which forms as a fused clinker in a ring surrounding with the upward flow of fuel and air and not infrequently result in burning out of the metal retort.

In the use .of other coals having a very difllcultly fusible-ash, the vash will not clinker, even at such high fuel bed temperatures, so that these coals, often of high heating value, are also not available for use in presently known stokers. I am aware of one commercial stoker which procoke formations. In the operation of the ,prior vld s m ns f r t r v f fi h y s ft n art stokers above-mentioned, certain coals would form such massive columns of coke in the combustion chamber of the retort as to clog the operatlon of the feed screw, or, if delivered from the upper end of said chamber by the lifting force of the incoming coal, would result in the deposit 0 large irregularly shaped pieces of coke upon the fuel bed closely surrounding the retort. Since these large coke pieces present a relatively small surface area in proportion to their weight, they 40 will burn very slowly. Consequently, to attain a desirably high over-all rate of burning with an efficiently low excess of air, a deep fuel bed must be built up. During periods of low heat demand it through a perforated grate surrounding the retort. The method of combustion, however, is the same as that above-described and it is an essential requisite to successful operation that extreme care be eaercised in selecting a coal that has such f 35 ash characteristics that it will not sinter or fuse together into pieces which are too large to pass through the grate.

Automatic stokers and methods of fuel combustion as heretofore developed have failed to meet requirements of. the practical art for many other reasons, among which the following may be enumerated:

' Dense smoke production after the heat demand it is not possible to maintain a live fuel bed and is satisfied and stoker operation stopped, due to frequent manual rekindling of the fire becomes necessary. Therefore, because of their strong coking characteristics, many of the high grade bituminous coals of greatest heating value are unthe continued evolution of volatile matter below the intensely hot combustion zone of the fuel .bed and absence of sufficient oxygen to burn the volatile gases; high velocity gases passing through suitable for use in automatic stokers now availthe combustion zone and carrying in suspension able.

Even the less strongly coking bituminous coals will form a. central column of coke which the air cannot penetrate so that the active burning area large pieces of unburned coke and ash which are deposited on the heat transfer surfaces and decrease the rate of heat transfer or are carried through the furnace stack and deposited on adis confined to an annular ring around the base of joining property to create a nuisance; non-flexibility or limitation of stoker operation to a comparatively small range of fuel types; inefficient heat radiation to transfer surfaces with high exit gas temperatures, and delayed response to thermostat control with continued delivery of heat to heating medium after stoker operation is stopped and failure to promptly answer the demand for heat due to the presence of large pieces of difiicultly ignit-able coke in the fuel bed.

Having the above-noted deficiencies of the prior art efforts in mind,it is the primary object and purpose of my present invention to provide a novel method and apparatus for burning solid carbonaceous fuels such as bituminous and anthracite coal, lignite and other varieties thereof and which will operate with equal efficiency in burning a selected type of fuel to convert a given quantity of such fuel into a maximumnumber of heat units with a minimum of unconsumed residue and the elimination of large clinker formations.

Another object of my invention resides in the provision of a method of burning fuel which will produce substantially uniform combustion over the entire fuel bed area and facilitate the radiation of heat to and its rapid absorption by the furnace heat transfer surfaces, so that the fuel bed temperature will be maintained at a sufficiently low point to effectively prevent excessive clinker formation.

The invention has for a further object to provide a novel method of fuel combustion particularly intended for use in connection with an automatic stoker of the under feeding type and which prevents the accumulation of large coke masses in the vicinity of the egress end of the retort chamber, so that there is a substantially unretarded feed of fuel from said chamber with a progressive outward horizontal movement of incandescent coke particles and ash whereby a desirably thin fuel bed with maximum heat radiation is maintained.

A further object of the invention is to provide, in one embodiment thereof, an annular circularly moving flame stream or curtain above the retort chamber, directed downwardly upon the fuel bed at a point in laterally spaced relation from the retort to create a turbulence in the upper end of said chamber and complete combustion of thevolatile gases emanating therefrom, so that the flame stream will produce a uniformly incandescent combustion zone in the fuel bed.

An additional object of the invention is to provide a fuel combustion method in which combustion air is so introduced into the fuel bed at such volume and velocity that substantial quantities of fly ash will not be carried through the furnace stack, and after stoker operation is stopped, admission of air to the fuel bed is continued and volatile gases therein consumed, thus preventing the emission of dense smoke clouds.

Another important object of the invention contemplates the provision of such a fuel burn ing method which will be reasonably responsive to thermostatic control and quickly discontinue or renew the active production of heat, beyond that required to maintain ignition, upon demand.

My present invention further includes a simply constructed, efficiently operating automatic stoker of the vertical feed screw type, one important object thereof being to provide means which will insure the maintenance of a' sumciently thorough agitation of the fuel particles in their upward movement through low tem- 4 perature throughout the major portion of the retort chamber to prevent large coke masses forming therein.

Another object resides in the provision of a flaring head at the upper end of the feed screw extending above the retort and positioned relative to the walls thereof so as to permit of the unrestricted delivery of fuel from the retort chamber, while cooperating with said walls to break up large coke formations and prevent the formation of coke trees.

A further object is to provide said head of the rotatable feed screw with a. tuyere located vertically above the retort wall and said head directing volatile gases to the tuyere toproduce a circularly moving flame stream impinging the fuel bed at a point in laterally spaced relation from the retort and directing the heated products of combustion toward the combustion chamber walls thereby providing highly emcient heat transfer relationships.

Another object of the invention is to provide means for preventing rotative movement of the incoming fuel with the feed screw to thereby facilitate its uniform upward movement through the retort and delivery therefrom to the fuel bed.

Other subordinate objects of my invention will become apparent from the following description when considered in connection with the accompanying drawings and the subjoined claims.

In the drawing, wherein I have illustrated one' concrete example of a preferred embodiment of apparatus for carrying out my new method, and in which similar reference characters designate corresponding parts throughout the several views:

Figure 1 is a side elevation, partly in section, of an automatic stoker similar to that disclosed in my pending application but modified to incorporate the principles of combustion of my present invention. In this view I have illustrated a typical coking bituminous coal with the approximate form of flame stream obtained from the rotating tuyere durin the "on" period of the stoker.

Figure 2 is a fragmentary vertical section showing the fuel bed and tuyere flames as they would appear during the off period, when burning a typical coking bituminous coal.

Figure 3 is a view similar to Figure 2 showing the fuel bed and rotating flame stream as they appear during the on eriod of the stoker when burning non-agglomerating fuels such as lignite or anthracite.

Figure 4 is a vertical sectio al view of the lower portion of the retort, and

Figure 5 is a horizontal sectional view taken on the line 5-5 of Figure 4.

For the purpose of efficiently and economically practicing my new method of burning solid fuels I have disclosed a preferred embodiment of mechanical apparatus in which the fuel is fed upwardly through a hollow-walled retort to a flaring egress throat with which a flared head on the upper end of a vertical feed screw cooperates to continue the feed of the fuel in a lateral direction and in substantially uniform volume to the fuel bed. Means is provided for controllably proportioning the air required for complete combustion into two parts, one of which is supplied to the fuel bed through tuyres in the outer wall of the retort and in the rim of said head at the upper end of its flared portion. The remaining and greater part of the air for fuel combustion is supplied through the fuel bed supporting grate.

Preferably, the aggregate volume of air supplied through the two sets of tuyeres is restricted to that which is necessary to establish ignition of the fuel and to heat an agglomerating fuel to the plastic state before it is horizontally deflected in a relatively thin layer between the fixed retort and the flaring head. Upward pressure of the plasticized fuel against the head wall, as its direction of movement is abruptly changed from a vertical to ahorizontal course, creates shearing forces which act to break .up the plastic masses into comparatively small pieces of more or less uniform size and prevent their agglomeration into large, slow burning, clinker-forming coke masses.

The propelling force of the incoming fuel, discharging through the egress throat of the retort, continuously moves the small pieces of coke outwardly over the bed-supporting grate surrounding the retort and into the zone of intense combustion. The relatively small, substantially unl form size of the coke pieces assures a comparatively thin fuel bed so that complete combustion is obtained with a minimum excess of air.

Such a thin fuel bed having a large active area results in the very effective radiation of heat to the heat transfer surfaces of the furnace or boiler unit and precludes the generation of excessive fuel bed temperatures.

In the case of agglomerating fuels, the shearing forces above-referred to break the coke masses into small pieces of uniform size regardless of the coking characteristics of the particular fuel, so that the present invention may be used with a wide variety of such fuels. Lignite and anthracite, however, being essentially nonagglomerating', are fed to the fuel bed in substantially the size in which they are fed to the stoker retort.

The relatively low fuel bed temperatures, insuring freedom from clinkering or fusion of the ash, enable the ash to be easily sifted through the grate by intermittently rotating the same, and, if desired, the convenient removal of the ash from the ash pit by mechanical means.

An important feature of the present invention resides in the location of the tuyres in the retort wall and the rotating head of the fuel feed screw with respect to each other and in relation to the upper end of the egress throat of the retort. The arrangement of the tuyres, as herein disclosed, by controlling the supply of combustionair thereto in proper proportion to the admission of air through the grate, produces a said combustion zone to establish a zone of in-' tense combustion in the thin fuel bed and the rapid radiation of combustion gases. The heated products of combustion are also forced outward against the heat-absorbing surfaces adjacent the fuel bed to start their upward course in a heat transferring relationship of maximum eifectiveness. Absorption of heat from this portion of the fuel bed, as above-noted, obviates the retention of excessively high temperatures in the thin fuel bed.

Heretoiore. in the use of automatic s-tokers with agglomerating fuels which are fed up through a new method so that a thick fuel bed must be maintained to burn the fuel. Also, since air is admitted onlyaround the periphery of the central retort, combustion occurs in a narrow annular area around, the central coke mass resulting in clinkering and very "high fuel bed temperatures. I' have found that if too large a proportion of air is admitted through the flared head and retort, intense combustion may occur and cause large clinker formations. I avoid this by admitting the greater proportion of air required for combustion through the grate which distributes the burning area over the entire grate surface. In this manner I also avoid high velocities of air and combustion gases and prevent the emission of large quantities of-fiy ash from the furnace stack.

The tuyre ports in the rotating head are at 7 all times above the fuel bed, and, during periods when the blower of the stoker is inoperative, sufficient air is admitted by natural draft through said ports to effectively burn volatile matter re? leased from the fuel and thus prevent the emission of dense smoke.

In summary, the herein disclosed method, as distinguished from prior art practices, makes the eflicient operation of automatic stokers possible in the burning of a wide variety of solid-fuels, to provide a comparatively thin, active incandescent fuel bed which is substantially co-extensive with the grate area, withhighly eflicient heat transfer and' economical fuel consumption.

With more particular reference to the drawings, in Figure 1 thereof I have shown a typical installation of an automatic stoker in a residential heating furnace of the water type, which embodies the essential features of the present invention in a preferred mechanical form. However, my invention is equally adaptable for use in connection with steam -or warm air heating systems and for industrial as well as residential heating purposes.

In the illustrative example the hollow furnace wall M which provides the water circulation chamber ii is suitably supported at a required elevation above the floor or ground surface. The cylindrical grate-enclosing wall 62 of the stoker unit extends upwardly within the inner shell of the furnace wall ill and is provided at its lower end, internally thereof, with an annular ash receiving trough i3. This cylindrical-wall i2 may be connected with and supported by the centrally located vertical retort of the stoker in the manner disclosed in my pending application above-identifled.

The retort includes an outer cylindrical wall it and an inner wall it concentrically spaced from said outer wall and integrally, or otherwise, connected therewith by a plurality of circumferentially spaced, longitudinally elongated webs iii. The wall l5 extends upwardly from a relatively thick base I! having an axially located opening is therein and upon which the feed screw to be later described is rotatably supported.

The outer wall id of the retort extends below the base if of the inner wall to form a plenum chamber I9 having a bearingsupport 2d at the top thereof provided with one or more openings 2i affording communication between said chamber and the vertidally extending annular air space 22 between the retort walls I and i5. The chamber I8 is connected by the conduit 23 with a suitable fan or blower (not shown). The horizontal support is formed with a relatively thick bearing portion 24 for the feed screw drive shaft.

The retort walls It and I5 terminate at their upper ends on a common horizontal plane and support a fuel egress throat section 25 of the retort. Thisthroat section has an outwardly flared inner wall 26 integrally joined at its upper end by a narrow annular top wall 21 with the outer cylindrical wall 28, which is preferably of the same internal diameter as the body wall It of the retort. The lower ends of the walls 26 and 28 are interlocked with the walls M and it as shown in my pending application; The space 29 between the walls 26 and 28 forms a continuation of the annular air space 22.

Immediately below the top wall 2! of the throat section of the retort the outer wall 28 thereof is provided with radial tuyeres or ports 30 at circumferentially spaced intervals. At its lower end the wall 28 is formed with an outwardly projecting annular flange 38 having a continuous circumferential rib 32 on its upper face for a purpose which will be later explained.

Co-axially positioned within the fuel receiving chamber 33 of the retort the vertical feed screw 32 i is rotatably supported upon the base ll. The central stem or shaft of this screw is hollow forming an air chamber 35 and has external helical lifting flights 36 integrally formed therewith. Preferably, the upper end of the fuel lifting flights terminates substantially at the upper end of the retort wall l5 and the periphery thereof is in close clearance relation to the inner surface of said wall.

The lower end of the screw shaft or stem is formed with or secured to the bearing ring ti, seating on the upper surface of the base ii, and an integrally formed tubular gudgeon 38 which has close fitting rotative engagement in the opening is of said base. hollow screw 3t through the webs M of the gudgeon 38, and communication between the plenum chamber 19 and the interior of the hollow screw shaft 33 is between webs did of the gudgeon.

From the gudgeon the upper end of the screw driving shaft 39 extends downwardly through the bearing 24. The lower end of said shaft is operatively connected with the horizontal shaft ii, journalled in the lower end of the retort wall it, by means of the gears 42 and 63. The means for operating the shaft 6! does not constitute an essential feature of my present disclosure. Any desired actuating means for said shaft to transmit continuous rotation to the feed screw at a predetermined speed may be employed, such for instance as that described in my aforesaid pending application and herein generally indicated at sit.

Upon the upper end of the feed screw 34 a hollow head 45 is detachably interlocked therewith, as at 46, for unitary rotation with said screw. This head includes an elongated portion M flaring upwardly and outwardly from the shaft 35 in substantially parallel relation to the retort throat wall 26 and extending above the retort in an arc 48which spans the egress opening of the retort throat 25. Above said portion 4'! the head is formed with a cylindrical portion 49 which is fitted with a removable cap 50. At the juncture of the head portions 41 and 49 a narrow annular shoulder 5| is formed with the peripheral face 52 thereof obliquely inclined downwardly and inwardly toward the axis of the feed screw.

The shaft 89 drives the A plurality of tuyeres or ports 53, perpendicular to the face 52, extend through the head wall at circumferentially spaced intervals to direct air jets downwardly and outwardly from said head toward the fuel bed. I

'Solid carbonaceous fuel is fed to the lower end of the retort chamber 33 from the conduit 54. supplied from a bin or hopper, through a suitable connecting duct or passage 55.. The feed screw 56 in said conduit may be driven by any suitable means, such as the sprocket chain 5?, said screw operating means being more fully disclosed in my prior application. Preferably, to the feed screw shaft I secure an agitating blade 58 to assist in feeding the fuel into the passage 55, and prevent packing thereof in the lower end of the retort. The shaft is extended beyond said blade and provided with screw flights 59 reversibly placed with respect to the flights of the screw 58 so as to return fuel particles which'may pass the blade 58 to the inlet passage of the retort.

The fuel bed supporting grate 60 is, preferably. of the well known sectional interlocking construction and surrounds the throat section 25 of the retort. While various means for supporting and intermittently rotating the grate may be employed, as in my prior invention, I preferably provide the grate sections with depending lugs 6i detachably fitting in sockets $3 on -a rotatable rin 62 of angular cross-sectional form. The vertical flange of this ring surrounds the retort wall Hi and any suitable type of anti-friction means St is interposed between the horizontal flange of said ring and the supporting flange 55 integrally formed with the retort wall.

Each grate section at its inner end has a groove 65 formed inits bottom face which loosely receives the guide rib 32 on the wall 28 of the retort throat, it being understood that the entire-weight of the grate is sustained by the ring 62. The horizontal flange of this ring projects beyond the stationary flange 65 and the underside thereof is provided with an annular series of rack teeth indicated at El with which a driving pawl coacts to intermittently rotate said ring and the grate relative to the retort. The pawl actuating mechanism, partially shown at 68, corresponds to that disclosed in my pending application and further detailed description thereof is not required for the purposes of the present explanation.

The ash falling through the openings of the grate 63 is received in the trough i3 and upon a pan 69 fixed to the rin 62 and rotating therewith. A number of spaced plow blades depend from the outer edge of the pan into the trough 3 to convey the ash collecting in said trough to the discharge tube 70 from which it is received by the conveyor screw ll operating in the conduit 12.

Ash which collects on the pan 69 is swept therefrom into the tube Ill by a blade 13 suitably fixed at one of its ends to the nner face of the cylindrical wall I2. The ash conveyor screw Il may be conven ently operated through suitable connecthe tuyeres 53 of the rotary head 65. The other vand larger proportion of the air is delivered through the grate openings to the fuel bed,

ings, in order to increase the coeflicient of friction between the fuel in chamber 33 and retort wall I5, I preferably provide said wall with rifling in the form of a plurality of spaced longitudinally extendin grooves 80 in its innersurface. Pieces of fuel catching in these grooves greatly increases the coeflicient of friction of the fuel on-the retort wall relative to the coeificient of friction on the retort to the tuyeres 30, through which it is discharged above the grate 80 in a plurality of comparatively low pressure air jets. Another part of the air from the blower flows upwardly through the hollow shaft 35 of the feed screw to the tuyeres53 of the rotating head 45 through which it is directed outwardly and downwardly upon feed screw, thus preventing rotation of the mass of fuel with the feed screw and insuring efficient, constantly uniform feeding of the fuel through the egress throat of the retort to the fuel bed.

'Thebody and throat sections of the .retort are preferably in the form of metal castings, and it will be noted that the walls I4 and I5 of the retort body are comparatively thin in relation to the walls of the throat section 25. These walls are of low heat conducting capacity so that there will be a minimum transmission of heat from the fuel bed to the green fuel moving upwardlythrough the retort chamber 33. Therefore, dense coking of the fuel in said chamber is obviated during the "off" period, and the riflings 80 on the wall IS insure a maximum lifting force on the coal column and the coke formations at the upper end thereof with positive delivery of the latter through the throat section 25 of the retort in an annular stream which is of substantially uniform density. Also, packing -of the coal in the lower end of the retort is thereby prevented. It will be noted that the cross-sectional area of the upwardly moving annular fuel column remains substantially the same at all points between the ingress and egress ends of the retort chamber 33. g

The objects of my new methodof burning solid fuels are attained in the operation of a stoker apparatus of the above description in the following manner:

With reference to Figure l of the drawings, the feed screw 56 is operated at a predetermined speed, in accordance with the particulartype of fuel, to feed the fuel from the storage bin or hopper through conduit 54 to the retort inlet 55,

the fuel being agitated and directed through said inlet by the blade 58. In the retort chamber 33 the annular column of fuel is elevated or lifted at a substantially constant or uniform speed by the feed screw 34 as its rotation around said screw is 4 arrested or retarded by the riflings 80. Thus the individual fuel particles will be uniformly fed up wardly under maximum lifting pressure through the retort, and in view of the low heat conductivity of the walls l4 and I5, transmission of heat from the fuel bed to the green fuel is minimized and formation of coke masses of any appreciable size in the retort chamber is effectively prevented.

Assuming that a flre has been started on the grate 60 by wood or other easily ignitable kindling material, the fuel is continuously fed thereto in the rotation of feed screw 34, the annular fuel column moving unrestrictedly upwardly through the throat section 25 of the retore between the wall 26 thereof and the parallel peripheral surface of the tapered lower portion 41 of the rotating head 45. Part of the air supplied by the blower through conduit 23 flows upwardly through the annular spaces 22 and 29 of the the fuel bed at a point in outwardly spaced relation from the top wall 21 of the retort. The latter air expanding in the highly heated head 45 acquires a somewhat greater velocity than the air supplied to the tuyres 30.

The air pressure jets from the tuyres 30 and 53 and volatile gases evolved from the fuel in the retort section 25 form a. combustible mixture at the tuyeres 53 where they ignite to form an annular flame sheet or stream F continuously moving in a circular path with the rotating head 45. This flame sheet and the burning fuel in .the bed maintain a plastici' ing zone temperature immediately above and within the egress end of the retort throat 25, the heat of the fuel ignited thereby flowing backward by conduction and radiation to the fuel column moving through the retort egress to heat the same to a temperature of substantially 700 to 800 F. At these temperatures agglomerating fuels, such as bituminous coals, are plasticated and tend to flow or fuse together in large masses.

However, it will be noted that in the present method, under the pressure of the incoming fuel moving upwardly through the retort, these agglomerated masses are moved upwardly above the retort throat 25 and forced under pressure against the over-hanging arcuately curved section 48 of the head 45. By providing an egress pasage through the retort throat which is of substantially uniform area, the fuel column tends to continue its upward movement in a straight line above the top of the retort. Thus, all large pieces of agglomerated coal will be subjected to the shearing pressure of the arcuate wall 48 of the rotating head which extends radially outward slightly beyond the prolongation of the the rotating head 45 is somewhat greater than the egress opening of the retort throat 25 and the tuyeres 53 are located vertically above the top wall 21 of said throat in such spaced relation therefrom that large agglomerated masses of fuel cannot collect upon the wall 21 and obstruct the emission of air from the tuyres 53.

As additional air flows between the plastic pieces of fuel, from the tuyeres 30, they are rapidly transformed into coke and this coked fuel is continuously moved radially outward in a uniformlythin bed over the rotatable grate where it is burned by the air flowing upwardly through the performations of the grate '60.

, The downwardly directed flame sheet F, impinging upon the fuel bed substantially mid-way between the retort and the furnace wall ignite the volatile gases released from the burning coke 11 and uniformly directs the burning products of combustion outwardly and upwardly in the form of an annular flame mass F against the furnace wall. In this manner a very rapid and efficient transfer of heat to the water or other heating medium is realized with a minimum of heat losses through the furnace stack. In Figure l of the drawings I have shown the stoker apparatus in operation when burning a typical coking bituminous coal, such as Pocahontas No. 3. Tests have demonstrated that with this, or a similar fuel of comparable coking characteristics, a desirably thin fuel bed may be maintained, not over about four or five inches thick.

With the supply of air in proper proportionate amounts to the fuel bed supporting grate so and the tuyres 3t and 53, (usually between 20 and 50 percent excess over that theoretically required to burn the fuel), the bed will not extend to the tuyres 53 in the rotating head 35. Owing to the force of the air and flame sheet F impinging upon the central area of the fuel bed, the top of the bed usually presents a somewhat con-,

cave appearance as shown at A, extending outwardly and upwardly toward the furnace wall, as at B, while decreasing in thickness inwardly toward the rotating head, as indicated at 0. During on periods of the stoker this fuel bed is incandescent over substantially the entire area of the grate 6t.

Figure 2 illustrates the condition which exists during ofi periods of stoker operation, when the heat demand has been satisfied. During this period, air is supplied to the tuyeres it and 58 by natural draft, the volume thereof being controlled by proper adjustment of the damper plate 16. This air has free egress through the tuyeres 53 of the head id-which are unobstructed by the fuel bed and, mixing with the volatile, combustible gases rising from the green fuel in the top of the retort, ignites to produce the torch like flames F In this manner the fuel bed remains sufficiently incandescent to ignite the incoming fuel at the next heat demand period. Also, the backward flow of heat from. the bed to the retort increases the continued release of volatile gases from the fuel therein, to maintain the torch-like flames F If air was not freely emitted from the tuyres under natural draft, as in previous combustion methods, the volatile gases would be decomposed by the high fuel bed temperature and. dense smoke would be emitted through the furnace stack. On the other hand, my new method results in substantially smoke-free combustion during non-operating periods of the stoker.

Lignite and anthracite being non-agglomerating fuels burn with a different type of bed, but, in the operation of the present invention, with equally satisfactory results. Lignite, being a highly reactive fuel, burns rapidly and, with the same excess of air as used with bituminous fuel, provides a thinner fuel bed. Anthracite, al-

though not of exceptionally high reactivity, is of smaller size and, for this reason, the bed is also usually thin. With these fuels, the concave upper fuel bed surface formed with bituminous coals is not present. Because of the difference in size of the fuel pieces and their angle of repose the upper surface of the bed is of substantially continuously convex or mound-shaped form, as indicated at D in Figure 3 of the drawings, said bed gradually decreasing in thickness from the central retort to the furnace wall. As above explained in connection with the burning of bim- 1'2 minous coals the rotary air and flame sheet F forces the burning products of combustion outwardly against the furnace walls to produce the' same rapid and efllcient transfer of heat from such fuels to the heating medium.

The two most important characteristics which govern the suitability of a fuel for use in any stoker are the coking characteristics, which may be measured by the Tentative Standard of the A. S. T. M. for the free swelling characteristics of coal, and the clinkering characteristics which may be roughly measured by the ash-softening temperature. Extended research in connection with my present invention has established theability of the above-described stoker apparatus, operating in accordance with the principles of my new'method, to satisfactorily handle a wide variety of types of bituminous or anthracite coals, lignite and other fuels having comparable coking and clinkering characteristcs. For instance, by means of my invention I have successfully burned bituminous coals ranging in coking characteristics from a swelling number of one and onehalf to two to a maximum of nine. This included strongly coking coals from the upper Freeport seam of Pennsylvania, 9. highly volatile, strongly coking coal, and from the Sewall seam of West Virginia, a medium volatile, strongly coking coal, both of which it has been practically impossible to handle in the operation of stokers with heretofore known methods of combustion.

Stoker apparatus embodying the principles of my present invention has successfully burned, without the formation of sufiicient clinker to hinder operation, coals having ash softening temperatures of 2000 to 2100 R, which is about the minimum range found in coals of the United States, as well as coals having ash softening temperatures of 2800 to 2900 1ft, which is about the maximum for coals of the United States. By feeding the fuel from the egress end of the retort in a uniformly distributed stream of coke partie cles of comparatively small size upon a fuel bed which. with proper admission of air through the grate, does not appreciably exceed a thickness of five inches, and impinging the mobile flame stream F thereon, the volatile products of combustion will be rapidly released from said coke particles. As said combustion productsare continuously driven off and directed upwardly against the heat transfer walls of the furnace the ash residue will be sifted from the relatively low temperature fuel bed in the rotative movement of the grate, thus substantially obviating theformation of clinkers therein and maintaining the fuel bed at a substantially constant temperature during the.on" period of the stoker. Of course, the discharge of unconsumed fuel with the ash, through the grate openings, will be very slight.

The ashes are automatically collected and removed from the trough l3 and pan 69 in the manner above-described.

With my new method of combustion I am also able to successfully burn lignite, which is extremely difficult to handle by previously known combustion methods, primarily because of its light structure and the light fluify nature of its ash residue. With the high pressure air blast used in prior art stokers there is an excessive emission of this light ash from the fuel bed resulting in heavy deposits thereof on the heat abthose in the vicinity. In my combustion method 13 and improved apparatus the greater portion of the combustion air is distributed over the entire grate area so that velocities are substantially lower than in such prior methods and the emission of fly ash is greatly reduced.

One practical installation of stoker apparatus involving my new method of combustion which gave very satisfactory test results hada capacity of about 25 pounds of bituminous or anthracite coal or lignite per hour. The several primary parts of said apparatus had the following approximate dimensions: Inside diameter of the retort body inches flaring to about 6% inches at the top of the throat section; diameter of rotating head 6% inches at level of tuyeres which were at a 30 angle, 24 in number, equidistantly spaced and 1 inches above the top of the retort; diameter of combustion chamber 22 inches and its area 2.6 square feet. Of the rotating grate area, approximately thirty per cent was open for ash removal and air supply. The grate openings were about inch wide and averaged about 4 inches long.

I have found that by adjusting the ratio of -air supplied through the grate with respect to that supplied through the central fixed and rotating tuyeres a great variety of fuels having different coking characteristics can be satisfactorily han-' died by my new methods. Typical examples of i 14 dium will quickly diminish after the supply of fuel and the blower are shut 011. Thus a con-" tinued supply of heat beyond that necessary to substantially satisfy requirements is avoided. On the other hand, although the bed temperature falls quickly, the restoration thereof when the supply of fuel and air is resumed is very rapid, to thus quickly respond to a further heat demand.

In conducting the test above-referred to a comparison of photo-electric smoke recorders installed'on the furnace equipped with my new stoker apparatus and on a furnace equipped with a known commercial stoker, showed that in the operation of "the former, in accordance with the above-described method,- the density of smoke emission was markedly reduced during the period following the shutting off of fuel supply and air from the ,blower fan. Observation of gases rising from the fuel bed also showed that the emission of fly ash is substantially less when using the present method.

From the, foregoing description, when con-. sidered in connection with the accompanying drawings, it will be seen that I have devised a new method and apparatus for burning solid fuels, whereby automatic stoking with highly emcient heat transfer has been practically perfected, and may be easily adapted with equal facility for the burning of such fuels in both variation in air ratios when burning twenty-five pounds of fuel per hour maybe notedas follows: residential and industrial furnaces. The new 0 s T vest 081 can ype a u u mug Per Pound Grate Illinois No.6 Free Burning-.. 11,000 235 115 Sewoll Strongly Coking 14,000, 240 180 Lignite Non-coking 8,000 15 75 In the above examples the air through the grate had a pressure of 0.05 to 0. 10 inch of water while that through the tuyeres had a pressure of 0.50 to 1.0 inch of water. r

The rate of feed of the fuel to the combustion chamber in relation to the aggregate volume of air supplied to the tuyere orifices 30 and 53 is properly adjusted for each specific type of fuel so as to obtain susbtantial equilibrium between the rate of fuel feed and the rate-of combusition. Thus, no appreciable variation in fuel bed thickness will occur in the operation of the stoker apparatus.

With bituminous coals, ,the more strongly coking and less easily ignited fuels require that a larger percentage of the air be supplied through the tuyeres and a relativel smaller amount through the grate. With free burning fuels which are easily ignited, it is necessary to supply only a small proportion of the air through the I my present invention.

fixed and rotary tuyres. It has been found important to supply only sufficient air at the tuyeres to maintain ignition at the rotary head as an excessive amount of air delivered through the tuyeres will result in localized intense combustion at the egress throat of the retort so that clinkers may be formed. Despite the free-burning nature of lignite, it is necessary to supply approximately half of the air through the tuyres, as this fuel contains a large amount of moisture and is not readily ignitable.

Elince my method of combustion provides a comparatively thin fuel bed-its heat capacity will be small and, therefore, the rate of heat transfer from the fuel bed to the heating metherein. l

method is of particular advantage in residential heating where economy, flexibility, convenience of operation and freedom from the necessity of frequent manual attendance are factors of prime:

importance. Of course, certain re-arrangements of the several units of the apparatus abovedescribed may be necessary in order to adaptthe same for use in connection with different types of furnaces and this may be readily done without change in the principles of combustion constituting the primary novel characteristic of The term coal is used herein as a generic expression to include all varieties of fuel having combustion characteristics which aregenerally similar to those of bituminous, anthracite and lignite.

The invention may be embodied in other specific forms without'departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not, restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, arid all changes which come within the meaning and range of equivalenc of the claims are therefore intended to be embraced What is claimed and desired to be secured by United States Letters Patent is:

1. In combination with a furnace combustion chamber and fuel bed supporting grate, means for maintaining a comparatively thin, incandescent fuel bed on said grate, said means comprising a retort having an upper egress end ofprogressively increasing internal diameter extending above the rate, a feed screw rotatably mounted in said retort to feed an annular column of fuel upwardly therethrough, said screw terminating below the egress end of the retort, a. head mounted on the. upper end of said screw for. rotation therewith and including a lower tapering section within the egress end of the retort and substantially parallel to the wall thereof, a top section spaced above the retort and an intermediate connecting section flaring outwardly and upwardl across the egress end of the retort, said top section having a series of air supply openings directed downwardly toward the fuel bed to maintain a fuel plasticizing temperature adjacent the upper end of the fuel column, said top section of the head having a di ameter substantially equal to the egress opening of the retort to apply shearing forces to the plasticized fuel and said flaring section of the head directing the fuel particles radially over the fuel bed, and means for supplyin additional combustion air to the fuel bed.

2. The method of burning carbonaceous fuels which comprises feeding the fuel in columnar form to a furnace combustion chamber, heatin the fuel at the exit end of said column to a temperature at which said fuel plasticizers and agglomerates, urging the fuel column upwardly by the pressure of the incoming fuel and applying reactionary forces to the agglomerated fuel to direct it laterally under shearing pressure and thereby divide the agglomerated fuel into particles of substantially uniform siz to form a relatively thin fuel bed.

3. The method defined in claim 2, in which the reactionary forces are applied in a radial outward direction from the interior of the fuel column and substantially uniformly throughout the circumferential extent of the columnat the point of emergence of the plasticized fuel into the bustion chamber.

4. The method defined in claim 2, in which combustion air is supplied in predetermined relative proportions to the plasticizing zone of the fuel column and to the fuel bed in accordance with the coke and ash forming characteristics of the fuel, to maintain a substantially uniform thin fuel bed during progressive feeding of the fuel column and consumption of the fuel.

5. The method of burning carbonaceous fuel which comprises feeding the fuel in a vertical col umn to a furnace combustion chamber, producing a heating zone of relatively high temperature adjacent the exit end of said column and directing the heat towards the incoming end of the fuel column to effect plasticization of the fuel as it enters the combustion chamber, urging the fuel column upwardly by the pressure of the incoming fuel and applying reactionary forces to the agglomerated fuel to direct it laterally under com- I shearing pressure and thereby divide the agglomerated fuel into particles of substantially uniform size to form a relatively thin fuel bed, supplying air to said heating zone at such volume and pressure as to produce a flame stream impinging the fuel bed in outwardly spaced relation from the fuel column to render said bed incandescent over 7. The method of burning carbonaceous fuel in I stoker-fired furnaces which comprises underfeeding the fuel in an annular column of substantially uniform wall thickness, heating the fuel in the upper portion of said column to plasticizing temperature, breaking the plasticized fuel into particles of substantially uniform size by the application of reactionary shearing forces to the incoming fuel and distributing said particles radially outward over the furnace grate in a thin fuel bed by the pressure of the incoming fuel, supplying suflicient combustion air adjacent the top of the fuel column for mixture with volatile gases evolved therefrom to maintain an ignition flame above said fuel column and adjacent thereto, and supplying the balance of the air required for complete combustion of the fuel through the furnace grate.

8. The method defined in claim 7, which in cludes supplying the major volume of combustion air through the fuel bed and constantly agitating said bed during the on period of the stoher.

9. The method defined in claim 7, which includes introducing air by natural draft above the fuel bed during the off period of the stoker to minimize smoke emission.

H A. SMAN.

REFERENCES CE'EED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 214:,472 Teamer Apr. 15, 1879 707,364 Smead Aug. 19, 1902 733,432 Shafer July it, 1983 1,139,708 Neidergesaess May 18, 1915 1,449,633 Taylor ..;'Mar. 27, 1928 1,658,247 Lower et al. Feb. 7, 1920 1,717,923 Greene June 18, 1929 1,728,913 Baler Sept. 24, 1929 1,886,577 Ousdahl Nov. 8, 1932 1,910,233 Blair May 23, 1933 1,927,199 Banfleld Sept. 19, 1933 1,929,889 Heaton Oct. 19, 1933 1,967,661 Chapman July 24, 1934 1,982,372 Christianson Nov. 27, 1934 1,997,833 Roland Apr. 16, 1935 2,098,024 Bailey Nov. 2, 1937 2,241,129 Hathaway et al May 8, 1941 2,306,189 Schweickart et al. Dec. 22, 1942 2,362,127 Gehl Nov. 7, 1944 Certificate of Correction Patent No. 2,455,817. December 7, 1948. RALPH A. SHERMAN It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 39, before the word water insert hot; column 9, line 70, for retore read retort; column 10, line 71, for performations read perforations; column 11, line 46, for increases read insures; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 12th day of April, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

